Fraud detection on Kovan testnet

Hi everyone,
In our platform, users are using the test segment with various addresses. In other hand, they are violating our T&C.
When we are on Kovan, are there any solutions to figure the repetitive usage out?
Assume that we have a contract and we wanna find specific users who test our DApp, more than one time. Any ideas?
Thanks for your kind favor, beforehand.